"I would never put it in the power of any printer or publisher to suppress or alter a work of mine, by making him master of the copy" Thomas Paine, Rights of Man, 1792.
"The printer dares not go beyond his licensed copy" Milton, Aeropagetica, 1644.
Since time immemorial, unauthorized use and outright piracy of proprietary source material has been a source of lost revenue, confusion, and artistic corruption.
These historical problems have been compounded by the advent of digital technology. With it, the technology of copying materials and redistributing them in unauthorized manners has reached new heights of sophistication, and more importantly, omnipresence. Lacking objective means for comparing an alleged copy of material with the original, owners and litigation proceedings are left with a subjective opinion of whether the alleged copy is stolen, or has been used in an unauthorized manner. Furthermore, there is no simple means of tracing a path to an original purchaser of the material--something which can be valuable in tracing where a possible "leak" of the material first occurred.
A variety of methods for protecting commercial material have been attempted. One is to scramble signals via an encoding method prior to distribution, and descramble prior to use. This technique, however, is of little use in mass market audio and visual media, where even a few dollars extra cost causes a major reduction in market, and where the signal must eventually be descrambled to be perceived, and thus can be easily recorded.
Another class of techniques relies on modification of source audio or video signals to include a subliminal identification signal, which can be sensed by electronic means. Examples of such systems are found in U.S. Pat. No. 4,972,471 and European patent publication EP 441,702, as well as in Komatsu et al, "Authentication System Using Concealed Image in Telematics," Memoirs of the School of Science & Engineering, Waseda University, No. 52, p. 45-60 (1988) (Komatsu uses the term "digital watermark" for this technique). These techniques have the common characteristic that deterministic signals with well defined patterns and sequences within the source material convey the identification information. For certain applications this is not a drawback But in general, this is an inefficient form of embedding identification information for a variety of reasons: (a) the whole of the source material is not used; (b) deterministic patterns have a higher likelihood of being discovered and removed by a would-be pirate; and (c) the signals are not generally `holographic` in that identifications may be difficult to make given only sections of the whole. (`Holographic` is used herein to refer to the property that the identification information is distributed globally throughout the coded signal, and can be fully discerned from an examination of even a fraction of the coded signal. Coding of this type is sometimes termed "distributed" herein.)
Among the cited references are descriptions of several programs which perform steganography --described in one document as ". . . the ancient art of hiding information in some otherwise inconspicuous information." These programs variously allow computer users to hide their own messages inside digital image files and digital audio files. All do so by toggling the least significant bit (the lowest order bit of a single data sample) of a given audio data stream or rasterized image. Some of these programs embed messages quite directly into the least significant bit, while other "pre-encrypt" or scramble a message first and then embed the encrypted data into the least significant bit.
Our current understanding of these programs is that they generally rely on error-free transmission of the of digital data in order to correctly transmit a given message in its entirety. Typically the message is passed only once, i.e., it is not repeated. These programs also seem to "take over" the least significant bit entirely, where actual data is obliterated and the message placed accordingly. This might mean that such codes could be easily erased by merely stripping off the least significant bit of all data values in a given image or audio file. It is these and other considerations which suggest that the only similarity between our invention and the established art of steganography is in the placement of information into data files with minimal perceptibility. The specifics of embedding and the uses of that buried information diverge from there.
Another cited reference is U.S. Pat. No. 5,325,167 to Melen. In the service of authenticating a given document, the high precision scanning of that document reveals patterns and "microscopic grain structure" which apparently is a kind of unique fingerprint for the underlying document media, such as paper itself or post-applied materials such as toner. Melen further teaches that scanning and storing this fingerprint can later be used in authentication by scanning a purported document and comparing it to the original fingerprint. Applicant is aware of a similar idea employed in the very high precision recording of credit card magnetic strips, as reported in the Feb. 8, 1994, Wall Street Journal, page B1, wherein very fine magnetic fluxuations tend to be unique from one card to the next, so that credit card authentication can be achieved through pre-recording these fluxuations later to be compared to the recordings of the purportedly same credit card.
Both of the foregoing techniques appear to rest on the same identification principles on which the mature science of fingerprint analysis rests: the innate uniqueness of some localized physical property. These methods then rely upon a single judgement and/or measurement of "similarity" or "correlation" between a suspect and a pre-recording master. Though fingerprint analysis has brought this to a high art, these methods are nevertheless open to a claim that preparations of the samples, and the "filtering" and "scanner specifications" of Melen's patent, unavoidably tend to bias the resulting judgement of similarity, and would create a need for more esoteric "expert testimony" to explain the confidence of a found match or mis-match. An object of the present invention is to avoid this reliance on expert testimony and to place the confidence in a match into simple "coin flip" vernacular, i.e., what are the odds you can call the correct coin flip 16 times in a row. Attempts to identify fragments of a fingerprint, document, or otherwise, exacerbate this issue of confidence in a judgment, where it is an object of the present invention to objectively apply the intuitive "coin flip" confidence to the smallest fragment possible. Also, storing unique fingerprints for each and every document or credit card magnetic strip, and having these fingerprints readily available for later cross-checking, should prove to be quite an economic undertaking. It is an object of this invention to allow for the "re-use" of noise codes and "snowy images" in the service of easing storage requirements.
Despite the foregoing and other diverse work in the field of identification/authentication, there still remains a need for a reliable and efficient method for performing a positive identification between a copy of an original signal and the original. Desirably, this method should not only perform identification, it should also be able to convey source-version information in order to better pinpoint the point of sale. The method should not compromise the inner quality of material which is being sold, as does the placement of localized logos on images. The method should be robust so that an identification can be made even after multiple copies have been made and/or compression and decompression of the signal has taken place. The identification method should be largely uneraseable or "uncrackable." The method should be capable of working even on fractional pieces of the original signal, such as a 10 second "riff" of an audio signal or the "clipped and pasted" sub-section of an original image.
The existence of such a method would have profound consequences on piracy in that it could (a) cost effectively monitor for unauthorized uses of material and perform "quick checks"; (b) become a deterrent to unauthorized uses when the method is known to be in use and the consequences well publicized; and (c) provide unequivocal proof of identity, similar to fingerprint identification, in litigation, with potentially more reliability than that of fingerprinting.
In accordance with an exemplary embodiment of the invention, the foregoing and additional objects are achieved by embedding an imperceptible identification code throughout a source signal. In the preferred embodiment, this embedding is achieved by modulating the source signal with a small noise signal in a coded fashion. More particularly, bits of a binary identification code are referenced, one at a time, to control modulation of the source signal with the noise signal.
The copy with the embedded signal (the "encoded" copy) becomes the material which is sold, while the original is secured in a safe place. The new copy is nearly identical to the original except under the finest of scrutiny; thus, its commercial value is not compromised. After the new copy has been sold and distributed and potentially distorted by multiple copies, the present disclosure details methods for positively identifying any suspect signal against the original.
Among its other advantages, the preferred embodiments' use of identification signals which are global (holographic) and which mimic natural noise sources allows the maximization of identification signal energy, as opposed to merely having it present `somewhere in the original material.` This allows the identification coding to be much more robust in the face of thousands of real world degradation processes and material transformations, such as cutting and cropping of imagery.
The foregoing and additional features and advantages of the present invention will be more readily apparent from the following detailed description thereof, which proceeds with reference to the accompanying drawings.